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Background: In clinical practice, the glomerular filtration rate (GFR) is often estimated from plasma creatinine. Several studies have shown cystatin C (cys C) to be a better parameter for the diagnosis of impaired renal function. No data are available, however, on the performance of cys C in follow-up of patients, compared with creatinine. Also, comparisons of cys C with the Cockcroft and Gault (C&G) formula for estimation of GFR are few., Methods: Plasma samples were obtained from 93 consecutive patients seen for GFR determination and from 30 patients with diabetes mellitus type 2, of whom 23 were investigated a second time after 2 years. GFR was determined with [125I]iothalamate. Plasma creatinine was determined enzymatically and the creatinine clearance calculated according to C&G. Cys C was measured with a particle-enhanced immunonephelometric method., Results: GFR correlated with 1/cys C (r = 0.873) as well as with C&G (r = 0.876). The area under the curve (AUC) of the receiver operating curves (ROCs), a measure of diagnostic accuracy, for cys C (0.931) and C&G (0.938) were equal (P = 0.815) and both better than the creatinine AUC (0.848; P = 0.006). Bland and Altman analysis showed that the simple formula GFR = -4.32 + 80.35 x 1/cys C, derived from our data, gave more accurate (P < 0.0001) and more precise (P = 0.024) GFR estimates than obtained with the C&G formula. The day-to-day variation (biological +analytical) for cys C was small (3.1%, SD 2.51%) in diabetic patients. In the follow-up study in diabetic patients, cys C was the parameter which had the best correlation (r = 0.66) with changes in GFR., Conclusions: Cys C shows a high correlation with GFR. With a very simple formula, cys C gives a good estimate of GFR, more accurate and precise than C&G. Because biological variation is low, cys C gives also a good assessment of GFR changes during follow-up. Cys C is the preferred endogenous parameter for GFR.

A 3-centre study was done to analyse the results of 70 patients with end-stage renal disease caused by diabetic nephropathy and treated with CAPD. Fifty patients had insulin-dependent diabetes (mean age 42, mean duration of diabetes 24 yr); 20 had non-insulin-dependent diabetes (mean age 61, mean duration 15 yr). Total treatment time was 1563 months and ranged from one to 83 months (median 18). Patient survival was 86% at 1 yr and 33% at 4 yr. Technique survival was 87% and 63%. Cox's multiple hazard regression analysis showed that age above 45 yr (relative risk 2.2), systolic hypertension (2.6) and cardiac disease (2.2) at the start of CAPD were associated with shorter patient survival. Metabolic control was good. Haemoglobin rose during the first 3 months. Plasma creatinine concentration increased with time, probably due to the loss of residual renal function. HbA1c levels were in the normal range for 60% of the patients. Mean hospital stay was 42 days per year, 26 as a consequence of vascular complications and 16 due to peritonitis and catheter-related problems. We conclude that CAPD is a good renal replacement modality for patients with diabetic renal failure. The patient survival is dependent on age, systolic hypertension and cardiac disease at the start of CAPD.